BLOOD SINUSES OF THE CRANIUM. 975 



spending transverse sinus, and both communicate with the posterior spinal veins. 

 Each occipital sinus is an anastomosing channel between the upper and lower 

 extremities of the transverse sinus of the same side, and each receives a few inferior 

 cerebellar veins. 



Sinus Cavernosi. The cavernous sinuses lie at the sides of the body of the 

 sphenoid bone. Each sinus commences, anteriorly, at the medial end of the superior 

 orbital fissure, where it receives the corresponding ophthalmic veins, and it 

 terminates, at the apex of the petrous portion of the temporal bone, by dividing 

 into the superior and the inferior petrosal sinuses. Its cavity, which is irregular 

 in size and shape, is so divided by numerous fibrous strands that it assumes the 

 appearance of cavernous tissue ; and in its lateral wall are embedded the internal 

 carotid artery with its sympathetic plexus, the oculomotor, the trochlear, the 

 ophthalmic and maxillary divisions of the trigeminal and the abducent nerves. Its 

 tributaries are the ophthalmic vein, the spheno-parietal sinus and the inferior 

 cerebral veins, including the middle cerebral vein (O.T. superficial Sylvian vein). 

 It communicates with the opposite cavernous sinus by means of. the anterior and 

 posterior intercavernous sinuses ; with the pterygoid plexus, in the infra-temporal 

 fossa, by an emissary vein which passes either through the foramen ovale or through 

 the foramen Vesalii; with the internal jugular vein by small venous channels 

 rhich accompany the internal carotid artery through the carotid canal, and by the 

 tferior petrosal sinus ; with the transverse sinus by the superior petrosal sinus ; 

 id through the superior ophthalmic vein with the angular vein. 



The spheno-parietal sinuses are lodged in the dura mater on the under surfaces 

 the small wings of the sphenoid bone close to their posterior borders. Each sinus 

 communicates with the middle meningeal veins, receives veins from the dura mater, 

 and terminates in the anterior part of the corresponding cavernous sinus. 



Sinus Petrosi Superiores. Each superior petrosal sinus commences at the 

 apex of the petrous portion of the temporal bone, in the posterior end of the 

 corresponding cavernous sinus, and it runs backwards and laterally, in the attached 

 margin of the tentorium cerebelli, above the trigeminal nerve. It grooves the 

 superior angle of the petrous portion of the temporal bone, at the lateral end of 

 which it terminates in the transverse sinus, at the point where the latter is turning 

 downwards on the medial surface of the mastoid portion of the temporal bone. It 

 receives inferior cerebral, superior cerebellar, tympanic, and diploic veins. 



Sinuus Petrosi Inferiores. An inferior petrosal sinus commences at the 

 posterior end of each cavernous sinus ; it runs backwards, laterally, and downwards, 

 in the posterior fossa of the cranium, in a groove formed by the lower angle of 

 the petrous part of the temporal bone and the adjacent border of the basilar part 

 of the occipital bone, to the anterior compartment of the jugular foramen of the 

 same side, through which it passes. It crosses the last four cerebral nerves either 

 on their lateral or on their medial sides, and it terminates in the internal jugular 

 vein. Its tributaries include inferior cerebellar veins and veins from the internal 

 ear, which pass to it through the internal acoustic meatus, the aquaeductus cochleae, 

 and the aquseductus vestibuli. 



Emissaria. The emissary veins are veins which convey blood from the blood sinuses in the 

 interior of the cranium to the veins which lie outside the walls of the cranium. They may be 

 single veins, or plexiform channels surrounding other structures which are passing through the 

 walls of the cranium. 



(1) Frontal. In the child, and sometimes in the adult, an emissary vein passes from the 

 anterior end of the superior sagittal sinus through the foramen caecum. Its lower end divides 

 into two channels which either terminate in the veins of the roof of the nasal cavities or they 

 perforate the nasal bones and join the angular veins. 



(2) Parietal. The parietal emissary veins, one on each side, pass through the parietal foramina, 

 from the superior sagittal sinus to the occipital veins. 



(3) Occipital. An occipital emissary vein is only occasionally present. It passes from the 

 " connuens sinuum " through the occipital protuberance to one of the tributaries of an occipital 

 vein, and it receives the occipital diploic vein. 



(4) Condyloid. When the condyloid canals are present in the occipital bone each is traversed 

 by a condyloid emissary vein, which connects the lower end of the corresponding transverse sinus 

 with the plexus of veins in the sub-occipital triangle. 



(5) Emissary Plexus of the Foramen Ovale. This plexus surrounds the mandibular nerve, as 

 it passes through the foramen ovale, and connects the cavernous sinus with the corresponding 



